I think it’s mostly because they keep trying to push other services down your throat. For example, opening a link in Outlook opens it in Edge, even when your default browser is something else. I can’t use Edge for that link, I’m not signed into stuff there. So now, because of retarded decisions like that, Outlook actually is missing basic features that Hotmail in the 90s had.
Your basic components will be an old desktop you have lying around and two hard drives. Put the two hard drives in RAID 1 (mirroring) set with either a network share and/or FTP access to add/remove stuff from the array. The drives optimally should be the same size, but if they aren’t that is OK, the amount of redundant space available will the the size of the smaller of the two drives.
Depending on what you have lying around this might not cost you anything. However, if you are going to spend money anywhere it should be on the drives themselves. You probably don’t need anything fancy, just a pair of 5400RPM HDDs that are large enough to hold your data, plus some room to grow.
You can use any OS of your choosing as basically everything supports the requirements. Linux, Windows, and TrueNAS come to mind as viable options. You may or may not want a third, tiny, drive just to boot the OS, particularly for Windows, as it can make things easier. I personally use Linux for my basic NAS with SFTP access.
Myself, I don’t. Being a landlord has quite a bit of risk from awful tenants as well as quite a bit of effort to make it work well. I have a job, don’t want another, and don’t want the additional risk; my investments are thus elsewhere.
You know what your tenant get for paying your mortgage? Jackshit.
If you are truly getting nothing by renting, buy a home instead. If you respond by saying ‘but I don’t want to, or can’t because of x’, that is what you are paying for as a renter.